The major objective of this research is to explore endocrince hypotheses, using epidemiologic means, to explain why variation in hormonal and reproductive events is related to altered breast cancer incidence. The forthcoming, and final, year of the project will be devoted to analytic activities, all data having been collected by March 1, 1979. These activities include: a) with the results of the second morbidity survey of breast cancer in a defined population with detailed information on menstrual and reproductive event, performing an historical cohort analysis relating menstrual cycle patterns to breast cancer incidence, b) concluding an analysis of case-control study of breast cancer patients testing etiologic hypotheses related to drug consumption, with emphasis on those causing prolactin secretion, menstrual cycle patterns, recurrent gynecologic symptom, tissue hormone receptor status, c) further investigation of the relationship between weight change, breast cancer and menstrual events, and d) completion of clinical studies relating potentially carcinogenic hormone patterns to altered menstrual and reproductive events.